The ASQ developers recommend having both the parent and another adult providing care for the child separately complete ASQ questionnaires. Parents with mental illness may be able to observe their child and provide valid and reliable information despite their symptoms. If the parent is an involved parent, it would be ideal to complete the questionnaire with the parent via interview and to ask a child care provider or someone else who knows the child to complete one also. You wouldn’t expect the questionnaires to agree completely because children display different skills and behaviors in different settings, but you would get some sense about the child’s development and whether or not they needed extra supports or further evaluation. 

The answer to this question also depends on whether you are using ASQ-3 or ASQ:SE-2. For the ASQ-3, the level of support required to complete items is going to be very high with families with mental health or substance abuse concerns, but a professional could certainly support the process. For the ASQ:SE-2, another person could complete the tool (who has at least 15-20 hours per week contact with the child) to get another more objective perspective. However, it still is important to know how a parent with a mental illness is feeling/thinking about their child's behavior so that they can be provided with parenting supports, which in either of these cases could be a very high need.